1. Technical Field
The invention relates to wireless communication systems. In particular, the invention relates to pico-cell radios mounted on utility messenger strands.
2. Discussion of the Prior Art
Currently, cell phone connections are made using high-power radios that are installed on radio towers and that are back-hauled through high bandwidth connections, typically T1 lines, to the mobile carriers. These radio cells are powered through external power supplies from main power lines.
A cell based wireless communication system that is currently implemented for cell phone communication consists of at least a mobile station and a base station connected to multiple stationary radios and forward and reverse links between them. The geographical area to be covered by wireless communication is divided into various cells. The radio equipment, i.e. a base-station transceiver subsystem (BTS), is installed in each such cell. The BTS consists of five major blocks a radio frequency (RF) front-end, transceivers, modem processors, a controller, and a power supply. The RF front-end and transceiver form a stationary radio unit (RU) within the BTS. The rest of the blocks typically form the main unit (MU) of the BTS. The BTS also includes antennas. The antennas can be omni-directional, or directional if the cell is divided into sectors. Each sector may have its own transmitting and receiving antennas. Two antennas per sector are required for diversity reception, thereby minimizing the effects of fading and multipath. In cells where the communication capacity is high, more than one RF carrier signal can be transmitted. This again increases the number of antennas. In older, integrated BTS systems, the BTS cabinet is located on the ground or in a housing near a mounting structure, such as a pole or a tower. The antennas are mounted on top of the mounting structure. The BTS is connected to the antenna by a coaxial cable that is typically about 50 to 200 feet long, depending on the height of the tower and the location of BTS on ground. Due to the cable length, a significant amount of power is lost between the BTS and the antenna. To reduce the power loss, thicker power cables are used, typically ¾″ to 1″ in diameter, which increases cost. Even then, at the required frequency of transmission, the power loss is considerable. This leads to degradation of receiver sensitivity and a reduction in the final transmitted power. The maintenance of these BTS is done by having the maintenance personal drive out to the location (truck roll) to check and repair of any faults at the site. These truck rolls are very expensive.
FIG. 1 shows a prior art implementation of a more modern, cell-based communication system base station 100. In this typical system, the RU 110 is removed from the MU 105 and located closer to the antenna 120 to reduce the problem of power loss. The MU 105 is retained at the bottom of the mounting structure 130. Before up-conversion to RF, the signal is carried by the cable 140 from MU 105 to RU 110. Because the signal is a low frequency signal, the loss in the cable is minimized. On the receive side, the cable also carries a low frequency signal because the RF is converted to a low frequency in the RU 110 and passed to the MU 105 for onward transmission. The high power amplifier can be replaced by a lower power amplifier because the cable loss is reduced. This helps reduce the size and weight of the RU 110. The size of the MU 105 is also reduced because the radio unit is removed from it. Many RUs 110 can be connected to a single MU 105, which then acts as a main base station. One or more antennas 120 can be connected to each RU 110, depending upon the requirements. The RUs 110 can be made to operate in different frequencies, different power levels, and different protocols.
A direct current (DC) power line 170 supplies power to the RU 110 by means of external power supplies 150, converted from main power lines 160. These power lines 160, from a main power source, must be installed at the site for the power to be supplied to the external power supplies 150. This increases the cost of establishing the cell based system 100.
Recent advances in wireless implementation have included messenger strand mounted modems for static connectivity to homes, etc. These dedicated systems are used to connect a receiver to a transmitter, typically using a high speed bidirectional antenna. This helps set up back haul stations for providing high speed links to homes, etc., as described in the Smith U.S. Pat. No. 7,162,234, by using pole mounted separate antennas. The capability to act as a base station with the ability to transfer connection of portable/mobile wireless devices between adjacent strand mounted modems as the mobile wireless device customer moves from coverage location of one modem to another has not been thought of. Such a system will be invaluable if implemented to provide the coverage in inaccessible areas and hilly regions, where wireless dark areas exist due to the inability of the cellular wireless towers to provide the necessary coverage.